1. Field of the Invention
The present invention relates to methods of imparting color and ultraviolet protection to synthetic yarns or substrates. More specifically, the present invention is directed to a method of solution dyeing a polymeric material during polymerization to form a base color shade, and subsequently dyeing the polymeric material by either yarn dyeing or piece dyeing. Ultraviolet protection is also provided in the solution dyeing step, by introducing an ultraviolet stabilizing agent into the polymer. The base shade may then be transformed into a useful color pallet with enhanced lightfastness properties.
It is well known in the textile arts to use solution dyeing techniques in order to dispose colors integrally within polymeric fibers. Additionally, it is also well known in the art to provide an agent to impart ultraviolet protection to the substrate by the addition of an ultraviolet stabilizer, or other ultraviolet protective agent, in this process. Generally, the process involves adding some colorant, such as pigment or dye, into the polymerization process.
Another common dyeing technique is yarn dyeing, which simply entails dyeing the yarn before it is made into a fabric or substrate. Yarns may be dyed in skeins or packages. In skein dyeing, large, loosely wound skeins of yarn are placed in a vat for dyeing. In package dyeing, the yarn is wound onto a number of perforated tubes or springs, and the dye is circulated around and through the tubes to assure that the yarns have maximum contact with the dyestuff.
Piece dyeing is a technique generally used when fabrics are to be dyed one solid color. In piece dyeing, the finished fabric is passed through a dyebath in which the fabric absorbs the dyestuff. Piece dyeing includes such methods as beck dyeing, jet dyeing, jig dyeing, beam dyeing, pad dyeing, vacuum impregnation, and foam dyeing, among others.
The solution dyeing technique is known to produce very colorfast materials, because the color is locked into the polymer itself. However, the number of yarn styles and colors that are solution dyed is limited for economic reasons. The fiber manufacturer must produce substantial quantities of fiber to justify the expense of adding an extra step during the manufacturing process. Furthermore, fiber production takes place well in advance of the time when fabrics reach the market. Fashion color trends may change fairly rapidly, so that, by the time a solution dyed fabric reaches the market, the color may be out of fashion. For these reasons, solution dyed fabrics are generally basic large volume styles and colors constructed from standard yarns.
Piece dyeing and yarn dyeing offer more color flexibility than solution dyeing, because these processes are further downstream in the manufacturing process. Because these methods tend to impart dyestuff to the outer portions of the yarn or substrate, and the color is not integrated within the polymeric structure, the colorfastness level is not as high as those levels achieved by solution dyeing.
Therefore, it would be desirable to provide a method of coloring a substrate that would allow substrates to be dyed in a wide variety of colors, and would provide a high level of colorfastness (and particularly lightfastness). Further, it would be desirable to provide a method of coloring substrates where the inventory of solution dyed substrates would consist of a few base shades that could be transformed by other dyeing methods into a wide variety of colors and shades. This method would reduce waste in the form of unused solution dyed substrates, obsolete yarn, and would allow reduced lead times on customer color orders. Additional benefits would include reduced inventory carrying costs and reasonable economies of scale in yarn production.
2. Description of the Prior Art
All U.S. patents referenced below are incorporated herein by reference, in their entirety.
U.S. Pat. No. 4,902,787, issued to Freeman, discloses a method of producing a UV lightfast disperse dyestuff comprising selecting a disperse dyestuff having predetermined chromophoric groups, selecting a photostabilizer compound, designing a hybrid disperse dye molecular structure which contains the chromophoric groups of the selected disperse dyestuff and also contains the molecular strucrural features of the selected photostabilizer compound, and synthesizing the thus designed hybrid disperse dyestuff molecule. This method produces a hybrid dye molecule which is a UV lightfast analog of a disperse dyestuff having predetermined chromophoric groups, where the hybrid dye molecule contains in its molecular structure the chromophoric groups of the selected disperse dyestuff and also contains the molecular structural features of a photostabilizer compound.
U.S. Pat. No. 5,376,151, issued to Freeman, et al., teaches methods for both the synthesis of metallized dyes and the generation of black dyeings using those dyes without employing metals designated as priority pollutants. The problems addressed in this reference are associated with the use of Cr-based metallized azo dyes to deliver black shades on natural and synthetic substrates. The key element of the disclosure is the use of black 1:2 Fe complexes of azo dyes in lieu of currently used Cr-based complexes which are based on environmentally unfriendly priority pollutant metals without compromising the desirable high fastness properties of the latter complexes.
U.S. Pat. No. 5,478,603, issued to Smith, is directed to an improved process for providing fibrous polyamide materials and wool materials with stain resistance and superior lightfastness that are more durable against alkaline washing. This is accomplished by treating the materials with an aqueous solution comprising a combination of a partially sulfonated novolak resin, methacrylic polymer and a soluble aluminum compound or a combination of a partially sulfonated novolak resin and a soluble aluminum compound.
None of the prior art, however, utilizes a combination of internal or solution dyeing with an external dye technique such as yarn dyeing or piece dyeing to produce a yarn or substrate having improved lightfast characteristics relative to external dyeing techniques alone. Further, none of the prior art offers a solution to the economic problems associated with the production of solution dyed yarn, as discussed above, particularly regarding the problems of waste, inefficiency, obsolescence, and inventory.